CA1054785A - Electrical discharge device comprising an insulator body having an electrically semi-conducting coating formed thereon - Google Patents
Electrical discharge device comprising an insulator body having an electrically semi-conducting coating formed thereonInfo
- Publication number
- CA1054785A CA1054785A CA217,913A CA217913A CA1054785A CA 1054785 A CA1054785 A CA 1054785A CA 217913 A CA217913 A CA 217913A CA 1054785 A CA1054785 A CA 1054785A
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- CA
- Canada
- Prior art keywords
- oxide
- weight
- coating
- conducting
- electrically semi
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
- H01T13/00—Sparking plugs
- H01T13/52—Sparking plugs characterised by a discharge along a surface
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K1/00—Printed circuits
- H05K1/02—Details
- H05K1/09—Use of materials for the conductive, e.g. metallic pattern
- H05K1/092—Dispersed materials, e.g. conductive pastes or inks
Abstract
ABSTRACT OF THE DISCLOSURE
An electrical discharge device and in particular a low voltage or shunt-type igniter plug is disclosed, the plug having a beryllium oxide ceramic insulator disposed between the center electrode firing tip and the ground electrode.
The insulator has a novel semi-conducting metal oxide coating formed thereon to provide an ionized path along which spark dis-charge between said electrodes occurs. The coating comprises a sintered mixture of lanthanum oxide and cuprous oxide, the coating being in electrical contact with said opposed electrodes and forming a bridge across the spark gap.
An electrical discharge device and in particular a low voltage or shunt-type igniter plug is disclosed, the plug having a beryllium oxide ceramic insulator disposed between the center electrode firing tip and the ground electrode.
The insulator has a novel semi-conducting metal oxide coating formed thereon to provide an ionized path along which spark dis-charge between said electrodes occurs. The coating comprises a sintered mixture of lanthanum oxide and cuprous oxide, the coating being in electrical contact with said opposed electrodes and forming a bridge across the spark gap.
Description
Background of the Invention Electr.cal discharge devices, such as igniter plugs, particularly those intended for use in aircraft engines of the jet or internal combustion types, are sub~ect to a number of environmental extremes, extremes of temperature being probably the severest factor to which an igniter plug and its components are subjected. If the plug is of the high-voltage type, generally about 15,000 to 25,000 volts are required to cause an electrical discharge across the spark gap, which high voltages further aggravate the hostility of the environment to which the plug is exposed. Moreover, due to difficulties in properly insulating high voltage systems, flashover problems between ad~acent components, in the electrical cable and in the ignition system itself are frequently encountered.
Consequently, low voltage, i.e., from about 1,000 to S,OQ0 volts, ignition systems have been developed, which systems require the use of a low voltage or shunted gap-type igniter plug, which is supplied with low voltage, high energy from a capacitor discharge system. In a shunt-type plug, the gap between the center electrode and the outer shell or ground electrode is bridged by a semi-conducting ceramic material which when pulses at low voltage allows the stored energy from the capacitor to ~, mjp/
; 1054785 discharge to ground across the igniter plug tip. Thus the ceramic tip which comprises the bridge member must possess certain physical and electrical characteristics to function properly in the environmental extremes created in modern engines and, in particular, jet aircraft engines.
In general, shunted ceramic tips are of two varieties, a surface treated insulator and the homogenous type wherein the entire insulator is a semi-conductor. An example of the former is described in U.S. Patent No. 2,953,704, wherein an aluminum oxide ceramic insulator is coated with a sintered mixture of cuprous oxide and ferric oxide. An example of the latter is described in U.S. Patent No. 3,558,959, wherein a semi-conducting ceramic body is formed of bonded particles of silicon carbide.
In the continuing search for improved materials to resist heat, thermal shock, spark erosion, and in general the hostile environment of modern engines, insulators comprised essentially of beryllium oxide have been found to be superior to more commonly used aluminum oxide insulators, both with respect to improved thermal conductivity and resistance to thermal shock. However, semi-conducting coatings developed for aluminum oxide based ceramics have proven unsatisfactory when applied to beryllium oxide ceramics. The present invention relates to an electrically semi-conducting coating composition suitable for coating beryllium oxide electrical insulators, the coating composition consisting essentially of a mixture of from 25 to 90 percent by weight of lanthanum oxide, from 5 to 75 percent by weight of cuprous oxide and from 0 to 25 percent by weight of ferric oxide.
In a further aspect the present invention relates to a beryllium oxide ceramic insulator body having an electrically semi-conducting coating formed thereon and bonded thereto, the B~
jvb/rw coating comprising a sintered mixture of lanthanum oxide and cuprous oxide.
In a still further aspect the invention is used in a shunt-type igniter plug comprising an outer metal shell, a ground electrode integral with said shell, a central electrode having a firing tip, said central electrode mounted in an in-sulator disposed within said shell, the firing tip of said cen-tral electrode being in opposed spaced relation to the ground electrode forming a spark gap therebetween, and provides improved electrically semi-conducting means adjacent said spark gap and in electrical contact with the opposed electrodes. The improved electrically semi-conducting means comprises a beryllium oxide ceramic body disposed about the central electrode. The ceramic body has formed thereon and bonded thereto an electrically semi-conducting coating, the coating comprising a sintered mix-ture of lanthanum oxide and cuprous oxide. The coating is in electrical contact with said opposed electrodes and forming a bridge across said spark gap.
The features of the invention will become apparent from the following description with reference to the accompanying drawings which are illustrative only of preferred embodiments of the invention.
Description of the Drawings Figure 1 is a partially schematic view, in longitudinal cross section, of the lower tip portion of an igniter plug em-bodying the invention; and Figure 2 is a view similar to Figure 1, showing a differently configured lower tip portion of an igniter plug embodying the invention.
jib/jvb Description of the Invention With reference to Figure 1, a low-voltage igniter plug 10 comprises a hollow, cylindrical body shell 11 which is generally made of a nickel-steel alloy. The lower extremity of shell 11 is formed as a radially inwardly directed flange 12.
The inner edge surface 13 of flange 12 is cylindrical and coaxial with the shell 11, which surface 13 of flange 12 constitutes a ground electrode. A central electrode 14 extends longitudinally within the shell 11 and is coaxial therewith, the firing tip 15 of the - 3a -A~ jib/jvb electrode 14 terminating in spaced relationship with the surface 13 thus forming an annular spark gap 16. When the plug 10 is installed in an engine, the flanged portion 12 is in direct communication with the combustion chamber of the engine and is grounded to the engine by contact between the shell 11 and the engine block. The upper end of central electrode 14 is seated in an annular insulating member 17 disposed within the shell 11 which insulates the central electrode 14 from the shell 11. The insulating member 17 may be formed of any suitable insulating material such as porcelain, borosilicate glass, aluminum oxide ceramic, beryllium oxide ceramic or the like. Another insulating member 18, formed principally of beryllium oxide, is annularly disposed abou~ the lower end of the central electrode 14, and extends from the lower end of insulating member 17 to the upper radially inwardly directed surface of th.e flange 12. The lower periphery and the lower face of the insulating member 18 is coated ~ith a semi-conducting layer 19, said layer 19 being in intimate contact with the lower end of the central electrode 14 and the upper surface of the radially inwardly directed flange 12, whereby current flow can occur across the semi-conducting coating 19 upon the application of low voltage, the current flow resulting in ionization of the spark gap 16, thus enabling a high energy, low voltage spark to discharge across the gap 16 and between the firing tip 15 of the central electrode 14 and the surface 13 of flange 12.
With reference to Figure 2, a low voltage igniter plug 20 comprises a hollow, cylindrical body shell 21. The lower extremity of body shell 21 is formed as a radially inwardly directed flange 22, the inner edge surface 23 of which is cylindrical and coaxial with the shell 21 which surface 23 o~
mjpl lOS4785 flange 22 constitutes a ground electrode. A central electrode 24 extends longitudinally within the shell 21 and coaxial there-with, the lower end of electrode 24 terminating in an annular, outwardly directed flange 25, said flange 25 having a lesser diameter than the diameter of radially inwardly directed flange 22 of shell 21, said flanges defining between them an annular spark gap 26. The upper end of central electrode 24 is seated in an annular insulating member 27 disposed within body shell 21, which insulates the central electrode 24 from the shell 21. The insulating member 27 may be formed of any suitable insulating material, such as porcelain, borosilicate glass, aluminum oxide ceramic, beryllium oxide ceramic or the like. Another insulsting member 28 formed principally of beryllium oxide is annularly disposed about the lower end of the central electrode 24 and extends from the lower end of insulating member 27 to both the -upper surface of flange 22 and the upper surface of flange 25, forming a bridge across the spark gap 26 formed between flange 25 and surface 23 of flange 22. The lower face of the insulating member 28 i8 coated with a semi-conducting layer 29, said layer 29 being in intimate contact with the upper surfaces o~ flanges 22 and 25, whereby current flow can occur along the semi-conduct-ing coating 29 upon the application of low voltage, the current flow resulting in ionization of the spark gap 26, thus enabling a high energy, low voltage spark to discharge across the gap 26 and between flange 25 of central electrode 24 and surface 23 of flange 22.
As described hereinabove, the electrically semi-conducting layer (designated at 19 in Figure 1 and at 29 in Figure 2~ which shunts the electrodes of the spark gap is in the form of a film-like coating formed on the beryllium oxide ceramic mjp/
insulator member. The semi-conducting layer is comprised of a fired mixture of lanthanum oxide (LazO3) and copper oxide, pre-ferably cuprous oxide (Cu20). The said mixture may also contain iron oxide, preferably ferric oxide (Fe2O9). The firing of the mixture of oxides is carried out at such temperature and for such length of time that at least one of the oxides is sintered, i.e.
heated to the point of incipient fusion. The liquid vehicle in which the oxides are preferably applied to the beryllium oxide substrate is driven-off or volatilized and the resulting electri-cally fiemi-conducting layer is compacted into a low resistance, smooth-surfaced coating layer which is firmly bonded to the surface of the beryllium oxide substrate.
In order to function satisfactorily in electrical discharge devices, such as low voltage igniter plugs, an electrically semi-conducting layer shunting the electrodes of such plugs must have a relati~ely smooth and unblemished outer surface confronting the gap; a relatively low resistivity both initially and during the life of the plug under the varying temperatures and other service conditions encountered during use; and must be well-bonded to the ceramic refractory substrate. Unless the semi-conducting layer is smooth and substantially free from imper-fections, it will not function uniformly over the area of the spark gap. Unless such layer is of relatively low resistivity, i.e. from about 10,000 to about 500,000 ohms, preferably from about 10,000 to about 100,000 ohms, it will not sufficiently strongly ionize the gap between the electrodes prior to spark discharge. Unless the layer is well-bonded to the ceramic sub-strate, it will flake or spall-off the substrate under prolonged, arduoùs service conditions.
It has been found that an electrically semi-conducting mjp/
coating material possessed of the above-mentioned desirable properties and suitable for coating predominantly beryllium oxide (i.e. from about 75% to 99% by weight BeO~ based ceramic insulator bodies comprises a sintered mixture of from 25% to 90% by weight lanthanum oxide (La203), from 5% to 75% by weight cuprous oxide (Cu20) and from 0% to 25% by weight ferric oxide (Fe20,). A
preferred semi-conducting coating comprises a sintered mixture of from 65% to 90% by weight lanthanum oxide (La203), from 10%
to 30% by weight cuprous oxide (Cu2O) and from 0% to 5% by weight ferric oxide (Fe20~).
The above ranges of weight percentages of the said oxides were determined by preparing about two hundred fifty mixtures of lanthanum, cuprous and ferric oxides of broadly varying compositions ranging from 0% to 100% by weight lanthanum oxlde, from 0% to 100% by weight cuprous oxide and from 0% to 100% by weight ferric oxide and coating each composition on individual beryllium oxide discs as will be more fully described hereinafter. The coated discs were fired at temperatures ranging from 2150F to 2450F and the resistance of the fired coatings was measured. The resistance values were plotted on ternary diagrams and correlated with the respective metal oxide com-position which yielded the respective resistance value. Metal oxide compositions in the above ranges were, from analyses of the ternary diagrams, found to produce coatings having acceptable low resistance properties and, a fortiori, would be suitable ln the preparation of electrically semi-conducting coatings particularly compatible with beryllium oxide ceramic substrates.
The coating is preferably prepared, generally speaking, by grinding the dry oxides to a fine powder and slurrying the same with a liquid media comprising water, a wetting agent and m~p/
a glycol. The oxide slurry is painted on the beryllium oxide substrate by brushing or spraying to a thickness of between about O.OOS to 0.010 inches (5 to lO mils). The coated substrate is then fired in a kiln or the like at a temperature of from about 2150F to 2450F until a smooth coated surface is obse{ved, the liquid carrier, of course, being volatilized. As the beryllium oxide is somewhat porous, the coating will to some extent pene-trate the pores, thus enhancing the adherence of the coating to the substrate.
The composition of preferred embodiments of electrically semi-conducting coatings on beryllium oxide ceramic substrates in accordance with the invention and a preferred manner of forming electrically semi-conducting coatings on beryllium oxide ceramic substrates are set forth in the following example, which example is intended solely for the purpose of illustration and is not to be construed as in any way limiting the scope of the invention.
A series of one-gram samples of lanthanum oxide (La20 Kerr-McGee, Code 528), cuprous oxide (Cu20~ Fisher C-477, Lot 723251) and ferric oxide (Fe203, Columbia 347 Grade) having the weight percentages indicated in Table l are prepared, each con-stituent of each sample being weighed, on a Mettler H15 (trade mark) analytical balance, to the nearest milligram. The dry oxides constituting each sample are ground together in a mortar and pestle and are placed in individual plastic vials. To each vial is added the following.
Glycerol................................... 3 drops Tergitol ~4 (trade mark for a wetting agent manufactured by Union Carbide Corp.) . 2 drops Distilled Water............................ 12 drops m~pl Note: The "drops" in which the volumes of glycerol, Tergitol #4 (trade mark) and water are given are drops from a standard -analytical burette.
The dry oxides are thoroughly mixed with the liquid additives to form a uniform slurry or suspension of the oxides in the liquit carrier. Each slurried sample is painted on a separate disc of beryllium oxide, each disc measuring approxi-mately 0.5 inches in diameter by 0.070 inches thick and having a 8eO content of about 99% by weight. To assure uniform appli-cation of each sample on each disc the following procedure isused.
Pressure sensitive masks or stencils are made by punching 0.25 inch diameter holes in masking tape, cutting off a section containing one hole and pressing the tape section onto a disc, positioning the hole in the center of the disc. Each sample is then painted, to a thickness of about 5 mils, over the hole in the tape section and when the mask is peeled away a 0.25 inch diameter sample is centered and coated on each disc.
The discs are then fired in an electrically heated resistance element-type kiln <Burrell, Model 90, trade mark) to the temperatures indicated in Table 1. The samples are heated at about 200F per hour to a temperature of about 800F to evaporate the liquid carrier after which heating is continued at a rate of about 400F per hour until the desired temperature is attained, Orton (trade mark) pyrometric cones being used to indicate the heat output and uniformity of firing. After firing, the discs are cooled and observed for smoothness and uniformity o coating. The resistance of the sintered coating is measured at 22C with a Simpson 260 ~trade mark) Ohmeter, the resistance for each sample at the respective firing temperature is tabulated in Table 1, in Ohms x 104.
m;p/ _g_ ~054785 As sllown by the data presented in Table 1, the semi-conducting metal oxide coating compositions according to the invention (Samples No. 1 through 22) each have satisfactory resistanceswhen coated on a beryllium oxide insulator material.
It will be observed that, generally speaking, the resistance of the coating increases with increasing firing temperature, and sig-nificantly increases at a firing temperature of 2450F, as exemplified by firing a number of said samples at that tempera-ture, which temperature of 2450~F is believed to be about the upper limit at which the coating can be fired and still retain satisfactory semi-conducting properties.
Samples ~o. 25 through 28 demonstrate that prior art semi-conducting coatings consisting of mixtures of cuprous oxide and ferric oxide, as taught in the aforementioned U. S. Patent No. 2,953,704, though satisfactory when coated on aluminum oxide ceramics~ are unsatisfactory when coated, as here, on a beryllium oxide ceramic, the coatings being electrically non-conducting in the latter instances.
Samples No. 30 and 31 are illustrative of the unsuit-ability of mixtures of lanthanum oxide and ferric oxide as coatingsprepared from mixtures of these oxides are also electrically non-conducting.
Samples No. 23, 24 and 29 are indicative of the unsuit-ability of coatings respectively consisting en~irely of lanthanum oxide, cuprous oxide or ferric oxide; satisfactory coatings being produced only when a mixture of lanthanum and cuprous oxides is employed or a mixture of these oxides plus ferric oxide, the presence of the latter believed to promote lower resistivity at higher lanthanum oxide ratios and appears to improve somewhat the adherence of the coating to the beryllium oxide substrate.
m~p/
It is to be further borne in mind that although the invention has been described with particular reference to its applicability to shunted gap-type igniter plugs, the inventive concept may be used in a variety of electrical semi-conducting applications, such as for example, in printed circuit patterns, high temperature resistors, grounding shunts for various electrical components and the like, which varying applications would be readily apparent to one skilled in the art, as the crux of the invention resides in providing an electrically semi-conducting coating that is suitable for application to a beryllium oxide ceramic insulating material. As regards the coating composition itself, it is to be understood that the use of ferric oxide as a constituent of the mixture is optional and is not critical to the formation of a satisfactory semi-conducting coating, the essential constituents of the coating being lanthanum oxide and cuprous oxide. In addition, although the metal oxide coating of the invention is particularly intended for application to beryllium oxide ceramic substrates, it may also be applied to insulating bodies composed of, for example, aluminum oxides.
m~p/
~OS4785 Ssmple Composition Resistance, Ohms x 104 at 22C
No. Percent by Weight After Firing at Indicated Temperature La2O~ CuzOFe2O32150F 2250F 2350F 2450F
Consequently, low voltage, i.e., from about 1,000 to S,OQ0 volts, ignition systems have been developed, which systems require the use of a low voltage or shunted gap-type igniter plug, which is supplied with low voltage, high energy from a capacitor discharge system. In a shunt-type plug, the gap between the center electrode and the outer shell or ground electrode is bridged by a semi-conducting ceramic material which when pulses at low voltage allows the stored energy from the capacitor to ~, mjp/
; 1054785 discharge to ground across the igniter plug tip. Thus the ceramic tip which comprises the bridge member must possess certain physical and electrical characteristics to function properly in the environmental extremes created in modern engines and, in particular, jet aircraft engines.
In general, shunted ceramic tips are of two varieties, a surface treated insulator and the homogenous type wherein the entire insulator is a semi-conductor. An example of the former is described in U.S. Patent No. 2,953,704, wherein an aluminum oxide ceramic insulator is coated with a sintered mixture of cuprous oxide and ferric oxide. An example of the latter is described in U.S. Patent No. 3,558,959, wherein a semi-conducting ceramic body is formed of bonded particles of silicon carbide.
In the continuing search for improved materials to resist heat, thermal shock, spark erosion, and in general the hostile environment of modern engines, insulators comprised essentially of beryllium oxide have been found to be superior to more commonly used aluminum oxide insulators, both with respect to improved thermal conductivity and resistance to thermal shock. However, semi-conducting coatings developed for aluminum oxide based ceramics have proven unsatisfactory when applied to beryllium oxide ceramics. The present invention relates to an electrically semi-conducting coating composition suitable for coating beryllium oxide electrical insulators, the coating composition consisting essentially of a mixture of from 25 to 90 percent by weight of lanthanum oxide, from 5 to 75 percent by weight of cuprous oxide and from 0 to 25 percent by weight of ferric oxide.
In a further aspect the present invention relates to a beryllium oxide ceramic insulator body having an electrically semi-conducting coating formed thereon and bonded thereto, the B~
jvb/rw coating comprising a sintered mixture of lanthanum oxide and cuprous oxide.
In a still further aspect the invention is used in a shunt-type igniter plug comprising an outer metal shell, a ground electrode integral with said shell, a central electrode having a firing tip, said central electrode mounted in an in-sulator disposed within said shell, the firing tip of said cen-tral electrode being in opposed spaced relation to the ground electrode forming a spark gap therebetween, and provides improved electrically semi-conducting means adjacent said spark gap and in electrical contact with the opposed electrodes. The improved electrically semi-conducting means comprises a beryllium oxide ceramic body disposed about the central electrode. The ceramic body has formed thereon and bonded thereto an electrically semi-conducting coating, the coating comprising a sintered mix-ture of lanthanum oxide and cuprous oxide. The coating is in electrical contact with said opposed electrodes and forming a bridge across said spark gap.
The features of the invention will become apparent from the following description with reference to the accompanying drawings which are illustrative only of preferred embodiments of the invention.
Description of the Drawings Figure 1 is a partially schematic view, in longitudinal cross section, of the lower tip portion of an igniter plug em-bodying the invention; and Figure 2 is a view similar to Figure 1, showing a differently configured lower tip portion of an igniter plug embodying the invention.
jib/jvb Description of the Invention With reference to Figure 1, a low-voltage igniter plug 10 comprises a hollow, cylindrical body shell 11 which is generally made of a nickel-steel alloy. The lower extremity of shell 11 is formed as a radially inwardly directed flange 12.
The inner edge surface 13 of flange 12 is cylindrical and coaxial with the shell 11, which surface 13 of flange 12 constitutes a ground electrode. A central electrode 14 extends longitudinally within the shell 11 and is coaxial therewith, the firing tip 15 of the - 3a -A~ jib/jvb electrode 14 terminating in spaced relationship with the surface 13 thus forming an annular spark gap 16. When the plug 10 is installed in an engine, the flanged portion 12 is in direct communication with the combustion chamber of the engine and is grounded to the engine by contact between the shell 11 and the engine block. The upper end of central electrode 14 is seated in an annular insulating member 17 disposed within the shell 11 which insulates the central electrode 14 from the shell 11. The insulating member 17 may be formed of any suitable insulating material such as porcelain, borosilicate glass, aluminum oxide ceramic, beryllium oxide ceramic or the like. Another insulating member 18, formed principally of beryllium oxide, is annularly disposed abou~ the lower end of the central electrode 14, and extends from the lower end of insulating member 17 to the upper radially inwardly directed surface of th.e flange 12. The lower periphery and the lower face of the insulating member 18 is coated ~ith a semi-conducting layer 19, said layer 19 being in intimate contact with the lower end of the central electrode 14 and the upper surface of the radially inwardly directed flange 12, whereby current flow can occur across the semi-conducting coating 19 upon the application of low voltage, the current flow resulting in ionization of the spark gap 16, thus enabling a high energy, low voltage spark to discharge across the gap 16 and between the firing tip 15 of the central electrode 14 and the surface 13 of flange 12.
With reference to Figure 2, a low voltage igniter plug 20 comprises a hollow, cylindrical body shell 21. The lower extremity of body shell 21 is formed as a radially inwardly directed flange 22, the inner edge surface 23 of which is cylindrical and coaxial with the shell 21 which surface 23 o~
mjpl lOS4785 flange 22 constitutes a ground electrode. A central electrode 24 extends longitudinally within the shell 21 and coaxial there-with, the lower end of electrode 24 terminating in an annular, outwardly directed flange 25, said flange 25 having a lesser diameter than the diameter of radially inwardly directed flange 22 of shell 21, said flanges defining between them an annular spark gap 26. The upper end of central electrode 24 is seated in an annular insulating member 27 disposed within body shell 21, which insulates the central electrode 24 from the shell 21. The insulating member 27 may be formed of any suitable insulating material, such as porcelain, borosilicate glass, aluminum oxide ceramic, beryllium oxide ceramic or the like. Another insulsting member 28 formed principally of beryllium oxide is annularly disposed about the lower end of the central electrode 24 and extends from the lower end of insulating member 27 to both the -upper surface of flange 22 and the upper surface of flange 25, forming a bridge across the spark gap 26 formed between flange 25 and surface 23 of flange 22. The lower face of the insulating member 28 i8 coated with a semi-conducting layer 29, said layer 29 being in intimate contact with the upper surfaces o~ flanges 22 and 25, whereby current flow can occur along the semi-conduct-ing coating 29 upon the application of low voltage, the current flow resulting in ionization of the spark gap 26, thus enabling a high energy, low voltage spark to discharge across the gap 26 and between flange 25 of central electrode 24 and surface 23 of flange 22.
As described hereinabove, the electrically semi-conducting layer (designated at 19 in Figure 1 and at 29 in Figure 2~ which shunts the electrodes of the spark gap is in the form of a film-like coating formed on the beryllium oxide ceramic mjp/
insulator member. The semi-conducting layer is comprised of a fired mixture of lanthanum oxide (LazO3) and copper oxide, pre-ferably cuprous oxide (Cu20). The said mixture may also contain iron oxide, preferably ferric oxide (Fe2O9). The firing of the mixture of oxides is carried out at such temperature and for such length of time that at least one of the oxides is sintered, i.e.
heated to the point of incipient fusion. The liquid vehicle in which the oxides are preferably applied to the beryllium oxide substrate is driven-off or volatilized and the resulting electri-cally fiemi-conducting layer is compacted into a low resistance, smooth-surfaced coating layer which is firmly bonded to the surface of the beryllium oxide substrate.
In order to function satisfactorily in electrical discharge devices, such as low voltage igniter plugs, an electrically semi-conducting layer shunting the electrodes of such plugs must have a relati~ely smooth and unblemished outer surface confronting the gap; a relatively low resistivity both initially and during the life of the plug under the varying temperatures and other service conditions encountered during use; and must be well-bonded to the ceramic refractory substrate. Unless the semi-conducting layer is smooth and substantially free from imper-fections, it will not function uniformly over the area of the spark gap. Unless such layer is of relatively low resistivity, i.e. from about 10,000 to about 500,000 ohms, preferably from about 10,000 to about 100,000 ohms, it will not sufficiently strongly ionize the gap between the electrodes prior to spark discharge. Unless the layer is well-bonded to the ceramic sub-strate, it will flake or spall-off the substrate under prolonged, arduoùs service conditions.
It has been found that an electrically semi-conducting mjp/
coating material possessed of the above-mentioned desirable properties and suitable for coating predominantly beryllium oxide (i.e. from about 75% to 99% by weight BeO~ based ceramic insulator bodies comprises a sintered mixture of from 25% to 90% by weight lanthanum oxide (La203), from 5% to 75% by weight cuprous oxide (Cu20) and from 0% to 25% by weight ferric oxide (Fe20,). A
preferred semi-conducting coating comprises a sintered mixture of from 65% to 90% by weight lanthanum oxide (La203), from 10%
to 30% by weight cuprous oxide (Cu2O) and from 0% to 5% by weight ferric oxide (Fe20~).
The above ranges of weight percentages of the said oxides were determined by preparing about two hundred fifty mixtures of lanthanum, cuprous and ferric oxides of broadly varying compositions ranging from 0% to 100% by weight lanthanum oxlde, from 0% to 100% by weight cuprous oxide and from 0% to 100% by weight ferric oxide and coating each composition on individual beryllium oxide discs as will be more fully described hereinafter. The coated discs were fired at temperatures ranging from 2150F to 2450F and the resistance of the fired coatings was measured. The resistance values were plotted on ternary diagrams and correlated with the respective metal oxide com-position which yielded the respective resistance value. Metal oxide compositions in the above ranges were, from analyses of the ternary diagrams, found to produce coatings having acceptable low resistance properties and, a fortiori, would be suitable ln the preparation of electrically semi-conducting coatings particularly compatible with beryllium oxide ceramic substrates.
The coating is preferably prepared, generally speaking, by grinding the dry oxides to a fine powder and slurrying the same with a liquid media comprising water, a wetting agent and m~p/
a glycol. The oxide slurry is painted on the beryllium oxide substrate by brushing or spraying to a thickness of between about O.OOS to 0.010 inches (5 to lO mils). The coated substrate is then fired in a kiln or the like at a temperature of from about 2150F to 2450F until a smooth coated surface is obse{ved, the liquid carrier, of course, being volatilized. As the beryllium oxide is somewhat porous, the coating will to some extent pene-trate the pores, thus enhancing the adherence of the coating to the substrate.
The composition of preferred embodiments of electrically semi-conducting coatings on beryllium oxide ceramic substrates in accordance with the invention and a preferred manner of forming electrically semi-conducting coatings on beryllium oxide ceramic substrates are set forth in the following example, which example is intended solely for the purpose of illustration and is not to be construed as in any way limiting the scope of the invention.
A series of one-gram samples of lanthanum oxide (La20 Kerr-McGee, Code 528), cuprous oxide (Cu20~ Fisher C-477, Lot 723251) and ferric oxide (Fe203, Columbia 347 Grade) having the weight percentages indicated in Table l are prepared, each con-stituent of each sample being weighed, on a Mettler H15 (trade mark) analytical balance, to the nearest milligram. The dry oxides constituting each sample are ground together in a mortar and pestle and are placed in individual plastic vials. To each vial is added the following.
Glycerol................................... 3 drops Tergitol ~4 (trade mark for a wetting agent manufactured by Union Carbide Corp.) . 2 drops Distilled Water............................ 12 drops m~pl Note: The "drops" in which the volumes of glycerol, Tergitol #4 (trade mark) and water are given are drops from a standard -analytical burette.
The dry oxides are thoroughly mixed with the liquid additives to form a uniform slurry or suspension of the oxides in the liquit carrier. Each slurried sample is painted on a separate disc of beryllium oxide, each disc measuring approxi-mately 0.5 inches in diameter by 0.070 inches thick and having a 8eO content of about 99% by weight. To assure uniform appli-cation of each sample on each disc the following procedure isused.
Pressure sensitive masks or stencils are made by punching 0.25 inch diameter holes in masking tape, cutting off a section containing one hole and pressing the tape section onto a disc, positioning the hole in the center of the disc. Each sample is then painted, to a thickness of about 5 mils, over the hole in the tape section and when the mask is peeled away a 0.25 inch diameter sample is centered and coated on each disc.
The discs are then fired in an electrically heated resistance element-type kiln <Burrell, Model 90, trade mark) to the temperatures indicated in Table 1. The samples are heated at about 200F per hour to a temperature of about 800F to evaporate the liquid carrier after which heating is continued at a rate of about 400F per hour until the desired temperature is attained, Orton (trade mark) pyrometric cones being used to indicate the heat output and uniformity of firing. After firing, the discs are cooled and observed for smoothness and uniformity o coating. The resistance of the sintered coating is measured at 22C with a Simpson 260 ~trade mark) Ohmeter, the resistance for each sample at the respective firing temperature is tabulated in Table 1, in Ohms x 104.
m;p/ _g_ ~054785 As sllown by the data presented in Table 1, the semi-conducting metal oxide coating compositions according to the invention (Samples No. 1 through 22) each have satisfactory resistanceswhen coated on a beryllium oxide insulator material.
It will be observed that, generally speaking, the resistance of the coating increases with increasing firing temperature, and sig-nificantly increases at a firing temperature of 2450F, as exemplified by firing a number of said samples at that tempera-ture, which temperature of 2450~F is believed to be about the upper limit at which the coating can be fired and still retain satisfactory semi-conducting properties.
Samples ~o. 25 through 28 demonstrate that prior art semi-conducting coatings consisting of mixtures of cuprous oxide and ferric oxide, as taught in the aforementioned U. S. Patent No. 2,953,704, though satisfactory when coated on aluminum oxide ceramics~ are unsatisfactory when coated, as here, on a beryllium oxide ceramic, the coatings being electrically non-conducting in the latter instances.
Samples No. 30 and 31 are illustrative of the unsuit-ability of mixtures of lanthanum oxide and ferric oxide as coatingsprepared from mixtures of these oxides are also electrically non-conducting.
Samples No. 23, 24 and 29 are indicative of the unsuit-ability of coatings respectively consisting en~irely of lanthanum oxide, cuprous oxide or ferric oxide; satisfactory coatings being produced only when a mixture of lanthanum and cuprous oxides is employed or a mixture of these oxides plus ferric oxide, the presence of the latter believed to promote lower resistivity at higher lanthanum oxide ratios and appears to improve somewhat the adherence of the coating to the beryllium oxide substrate.
m~p/
It is to be further borne in mind that although the invention has been described with particular reference to its applicability to shunted gap-type igniter plugs, the inventive concept may be used in a variety of electrical semi-conducting applications, such as for example, in printed circuit patterns, high temperature resistors, grounding shunts for various electrical components and the like, which varying applications would be readily apparent to one skilled in the art, as the crux of the invention resides in providing an electrically semi-conducting coating that is suitable for application to a beryllium oxide ceramic insulating material. As regards the coating composition itself, it is to be understood that the use of ferric oxide as a constituent of the mixture is optional and is not critical to the formation of a satisfactory semi-conducting coating, the essential constituents of the coating being lanthanum oxide and cuprous oxide. In addition, although the metal oxide coating of the invention is particularly intended for application to beryllium oxide ceramic substrates, it may also be applied to insulating bodies composed of, for example, aluminum oxides.
m~p/
~OS4785 Ssmple Composition Resistance, Ohms x 104 at 22C
No. Percent by Weight After Firing at Indicated Temperature La2O~ CuzOFe2O32150F 2250F 2350F 2450F
2 30 70 0 30 40 15
3 45 55 0 30 10 30
4 50 50 0 25 15 15 16 75 25 0 lO 7 15 22 85 10 5 lQ 10 20 50 23 100 0 0~nfiniteInfiniteInfinite 24 0 100 Infinite Infinite Infinite 0 92 8 Infinite Infinite Infinite 26 85 15 Infinite Infinite Infinite 27 0 75 25 Infinite Infinite Infinite 28 0 65 35 Infinite Infinite Infinite 29 O 100 Infinite Infinite Infinite 0 20 Infinite Infinite Infinite 31 90 0 10 Infinite Infinite Infinite mjp/
Claims (12)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a shunt-type igniter plug comprising an outer metal shell, a ground electrode integral with said shell, a central electrode having a firing tip, said central electrode mounted in an insulator disposed within said shell, the firing tip of said central electrode being in opposed spaced relation to the ground electrode forming a spark gap therebetween, and improved electrically semi-conducting means adjacent said spark gap and in electrical contact with the opposed electrodes, said improved electrically semi-conducting means comprising a beryllium oxide ceramic body disposed about said central electrode, said ceramic body having formed thereon and bonded thereto an electrically semi-conducting coating, said coating comprising a sintered mixture of lanthanum oxide and cuprous oxide, said coating being in electrical contact with said opposed electrodes and forming a bridge across said spark gap.
2. The igniter plug of Claim 1 wherein said electrically semi-conducting coating comprises a sintered mixture of lanthanum oxide, cuprous oxide and ferric oxide.
3. The igniter plug of Claim 2 wherein said electrically semi-conducting coating comprises a sintered mixture of from 25X to 90% by weight of lanthanum oxide, from 5% to 75% by weight of cuprous oxide and from 0% to 25% by weight of ferric oxide.
4. The igniter plug of Claim 3 wherein said electrically semi-conducting coating comprises a sintered mixture of from 65% to 90% by weight of lanthanum oxide, from 10% to 30%
by weight of cuprous oxide and from 0% to 5% by weight of ferric oxide.
by weight of cuprous oxide and from 0% to 5% by weight of ferric oxide.
5. The igniter plug of Claim 1 wherein said coating is applied to a thickness of from 0.005 to 0.010 inches.
6. A beryllium oxide ceramic insulator body having an electrically semi-conducting coating formed thereon and bonded thereto, said coating comprising a sintered mixture of lanthanum oxide and cuprous oxide.
7. The insulator body of Claim 6 wherein said coating comprises a sintered mixture of lanthanum oxide, cuprous oxide and ferric oxide.
8. The insulator body of Claim 7 wherein said coating comprises a sintered mixture of from 25% to 90% by weight of lanthanum oxide, from 5% to 75% by weight of cuprous oxide ant from OX to 25% by weight of ferric oxide.
9. The insulator body of Claim 8 wherein said coating comprises a sintered mixture of from 65% to 90% by weight of lanthanum oxide, from 10% by weight to 30% by weight of cuprous oxide and from 0% to 5% by weight of ferric oxide.
10. The insulating body of Claim 6 wherein said coating is applied to a thickness of from 0.005 to 0.010 inches.
11. An electrically semi-conducting coating composition suitable for coating beryllium oxide electric insulators, said coating composition consisting essentially of a mixture of from 25 to 90 percent by weight of lanthanum oxide, from S to 75 percent by weight of cuprous oxide and from 0 to 25 percent by weight of ferric oxide.
12. The coating composition of claim 1 consisting essentially of a mixture of from 65 to 90 percent by weight of lanthanum oxide, from 10 to 30 percent by weight of cuprous oxide and from O to 5 percent by weight of ferric oxide.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US480199A US3883762A (en) | 1974-06-17 | 1974-06-17 | Electrical discharge device comprising an insulator body having an electrically semi-conducting coating formed thereon |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1054785A true CA1054785A (en) | 1979-05-22 |
Family
ID=23907042
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA217,913A Expired CA1054785A (en) | 1974-06-17 | 1975-01-14 | Electrical discharge device comprising an insulator body having an electrically semi-conducting coating formed thereon |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US3883762A (en) |
| JP (1) | JPS5845148B2 (en) |
| CA (1) | CA1054785A (en) |
| DE (1) | DE2526836A1 (en) |
| FR (1) | FR2274578A1 (en) |
| GB (1) | GB1470482A (en) |
| IT (1) | IT1044572B (en) |
Families Citing this family (21)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4439707A (en) * | 1980-07-23 | 1984-03-27 | Nippon Soken, Inc. | Spark plug with a wide discharge gap |
| US4713574A (en) * | 1985-10-07 | 1987-12-15 | The United States Of America As Represented By The Secretary Of The Air Force | Igniter electrode life control |
| US4748947A (en) * | 1987-06-22 | 1988-06-07 | Ford Motor Company | Ignition system and method for multi-fuel combustion engines |
| JPH01163986A (en) * | 1987-12-18 | 1989-06-28 | Ngk Spark Plug Co Ltd | Low voltage surface discharge type ignitor plug |
| JPH01225085A (en) * | 1988-03-03 | 1989-09-07 | Ngk Spark Plug Co Ltd | Creeping discharge type spark plug |
| US5166574A (en) * | 1989-07-14 | 1992-11-24 | Yazaki Corporation | High-tension cable device |
| US5187404A (en) * | 1991-08-05 | 1993-02-16 | Cooper Industries, Inc. | Surface gap igniter |
| US6133146A (en) * | 1996-05-09 | 2000-10-17 | Scb Technologies, Inc. | Semiconductor bridge device and method of making the same |
| JP4089012B2 (en) * | 1997-09-24 | 2008-05-21 | 株式会社デンソー | Spark plug |
| DE19950922A1 (en) * | 1999-10-21 | 2001-04-26 | Beru Ag | spark plug |
| FR2881281B1 (en) * | 2005-01-26 | 2011-04-22 | Renault Sas | PLASMA GENERATION CANDLE |
| JP5072947B2 (en) * | 2008-12-26 | 2012-11-14 | 日本特殊陶業株式会社 | Spark plug and ignition system |
| FR2959071B1 (en) * | 2010-04-16 | 2012-07-27 | Renault Sa | SPARK PLUG EQUIPPED WITH MEANS FOR PREVENTING SHORT CIRCUITS |
| EP2652847B2 (en) * | 2010-12-14 | 2019-03-06 | Federal-Mogul Ignition Company | Corona igniter with improved corona control |
| WO2012092432A1 (en) * | 2010-12-29 | 2012-07-05 | Federal-Mogul Ignition Company | Corona igniter having improved gap control |
| WO2014179649A1 (en) | 2013-05-03 | 2014-11-06 | Federal-Mogul Ignition Company | Corona ignition with hermetic combustion seal |
| US9484717B2 (en) * | 2013-12-26 | 2016-11-01 | Chentronics, Llc | High energy ignition spark igniter |
| JP7051381B2 (en) * | 2017-11-16 | 2022-04-11 | 日本特殊陶業株式会社 | Spark plug |
| US10815896B2 (en) * | 2017-12-05 | 2020-10-27 | General Electric Company | Igniter with protective alumina coating for turbine engines |
| US10879677B2 (en) * | 2018-01-04 | 2020-12-29 | Tenneco Inc. | Shaped collet for electrical stress grading in corona ignition systems |
| CN109538357B (en) * | 2018-11-19 | 2021-01-01 | 陕西航空电气有限责任公司 | Small semiconductor electric nozzle structure and processing method |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2684665A (en) * | 1949-06-09 | 1954-07-27 | Bendix Aviat Corp | Electrical apparatus |
| JPS5132181B2 (en) * | 1971-10-14 | 1976-09-10 |
-
1974
- 1974-06-17 US US480199A patent/US3883762A/en not_active Expired - Lifetime
-
1975
- 1975-01-14 CA CA217,913A patent/CA1054785A/en not_active Expired
- 1975-05-12 GB GB1988475A patent/GB1470482A/en not_active Expired
- 1975-06-06 FR FR7517704A patent/FR2274578A1/en active Granted
- 1975-06-14 JP JP50072617A patent/JPS5845148B2/en not_active Expired
- 1975-06-16 DE DE19752526836 patent/DE2526836A1/en not_active Withdrawn
- 1975-06-16 IT IT24376/75A patent/IT1044572B/en active
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5113032A (en) | 1976-02-02 |
| FR2274578A1 (en) | 1976-01-09 |
| IT1044572B (en) | 1980-03-31 |
| US3883762A (en) | 1975-05-13 |
| FR2274578B1 (en) | 1977-07-08 |
| JPS5845148B2 (en) | 1983-10-07 |
| GB1470482A (en) | 1977-04-14 |
| DE2526836A1 (en) | 1976-01-02 |
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